M. E. Johnston

Molecular taxonomic clarification of Ptilotus exaltatus and Ptilotus nobilis (Amaranthaceae)

A complete botanical key for the genus Ptilotus R. Brown ( family Amarathaceae) has not yet been published. Identifying the 100 or more Ptilotus species using morphological characters has been difficult because plants often exhibit slight morphological differences and intermediate characteristics common to several species, subspecies, varieties and forms. Ptilotus exaltatus Nees and P. nobilis ( Lindl) F. Muell share many morphological characteristics, but are classified as different species predominantly based on inflorescence colour. The current study involved a molecular phylogenetic analysis of 14 Ptilotus species using sequence data from the internal transcribed spacer ( ITS) regions ITS 1 and ITS 2 within the 18S-26S nuclear rDNA. Of the 39 accessions analysed, all except those identified as P. exaltatus and P. nobilis clustered according to their respective species based on their morphological taxonomy. In contrast, all 18 P. exaltatus and P. nobilis accessions formed a distinct monophyletic clade with 99% bootstrap values and a low level of sequence variation ( GD=0.002). Taking into account the lack of reliable morphological characters for separating P. exaltatus and P. nobilis, together with the ITS sequence data showing little genetic divergence or genetic structure, we propose that P. exaltatus and P. nobilis are conspecific.

Modelling temperature, photoperiod and vernalization responses of Brunonia australis (Goodeniaceae) and Calandrinia sp (Portulacaceae) to predict flowering time

BACKGROUND AND AIMS Crop models for herbaceous ornamental species typically include functions for temperature and photoperiod responses, but very few incorporate vernalization, which is a requirement of many traditional crops. This study investigated the development of floriculture crop models, which describe temperature responses, plus photoperiod or vernalization requirements, using Australian native ephemerals Brunonia australis and Calandrinia sp. METHODS A novel approach involved the use of a field crop modelling tool, DEVEL2. This optimization program estimates the parameters of selected functions within the development rate models using an iterative process that minimizes sum of squares residual between estimated and observed days for the phenological event. Parameter profiling and jack-knifing are included in DEVEL2 to remove bias from parameter estimates and introduce rigour into the parameter selection process. KEY RESULTS Development rate of B. australis from planting to first visible floral bud (VFB) was predicted using a multiplicative approach with a curvilinear function to describe temperature responses and a broken linear function to explain photoperiod responses. A similar model was used to describe the development rate of Calandrinia sp., except the photoperiod function was replaced with an exponential vernalization function, which explained a facultative cold requirement and included a coefficient for determining the vernalization ceiling temperature. Temperature was the main environmental factor influencing development rate for VFB to anthesis of both species and was predicted using a linear model. CONCLUSIONS The phenology models for B. australis and Calandrinia sp. described development rate from planting to VFB and from VFB to anthesis in response to temperature and photoperiod or vernalization and may assist modelling efforts of other herbaceous ornamental plants. In addition to crop management, the vernalization function could be used to identify plant communities most at risk from predicted increases in temperature due to global warming.

Juvenility and flowering of Brunonia australis (Goodeniaceae) and Calandrinia sp (Portulacaceae) in relation to vernalization and daylength

BACKGROUND AND AIMS The time at which plants are transferred to floral inductive conditions affects the onset of flowering and plant morphology, due to juvenility. Plants of Brunonia australis and Calandrinia sp. were used to investigate whether Australian native ephemeral species show a distinct juvenile phase that can be extended to increase vegetative growth and flowering. METHODS The juvenile phase was quantified by transferring seedlings from less inductive (short day and 30/20°C) to inductive (vernalization or long day) conditions at six different plant ages ranging from 4 to 35 d after seed germination. An increase in days to first visible floral bud and leaf number were used to signify the end of juvenility. KEY RESULTS Brunonia australis was receptive to floral inductive long day conditions about 18-22 d after seed germination, whereas plants aged 4-35 d appeared vernalization sensitive. Overall, transferring plants of B. australis from short to long day conditions reduced the time to anthesis compared with vernalization or constant short day conditions. Calandrinia sp. showed a facultative requirement for vernalization and an insensitive phase was not detected. Floral bud and branch production increased favourably as plant age at time of transfer to inductive conditions increased. Younger plants showed the shortest crop production time. CONCLUSIONS Both species can perceive the vernalization floral stimulus from a very young age, whereas the photoperiodic stimulus is perceived by B. australis after a period of vegetative growth. However, extending the juvenile phase can promote foliage development and enhance flower production of both species.

Inhibition of adventitious rooting in Backhousia citriodora F. Muell. cuttings correlate with the concentration of essential oil

Summary Backhousia citriodora is typical of the many commercially valuable woody Australian Myrtaceae species that are recalcitrant in forming adventitious roots from cuttings after maturation. A series of experiments were conducted to identify an endogenous rooting inhibitor in line with established criteria. Endogenous levels of citral were correlated with the rooting capacities of juvenile versus mature, and easy- versus dificult-to-root genotypes of B. citriodora, in both winter and summer. The biological activity of citral was confirmed in bioassays on mung beans and easy-to-root B. citriodora seedlings. Evidence of a common mechanism of root inhibition with other species in the Myrtaceae and the role of action of citral are discussed.

HIGH IRRADIANCE INCREASES ORGANOGENESIS IN FRIABLE CALLUS OF CAUSTIS BLAKEI KUK. (CYPERACEAE)

SummaryCaustis blakei is an attractive cut foliage plant harvested from the wild in Australia and marketed under the name of koala fern. Previous attempts to propagate large numbers of this plant have been unsuccessful. The effect of four light irradiances on organogenesis from compact and friable callus of C. blakei was studied for 21 wk. Both callus types produced numerous primordial shoots but many failed to develop into green plantlets. However, significantly more primordial shoots and green plantlets developed on the friable callus than on the compact callus, and significantly more green plantlets were regenerated under the higher photon irradiances of 200 and 300 μmol m−2s−1 than under the lower irradiances of 100 and 150 μmol m−2s−1. The compact callus produced its maximum number of green plantlets early in the experiment (after 9 wk), while the friable callus continued to produce primordial shoots and green plantelets throughout the period of the experiment, and reached its maximum production of green plantlets at 21 wk under the irradiance of 300 μmol m−2s−1. Organogenesis from friable callus under high irradiance (300 μmol m−2s−1) offers an efficient propagation method for C. blakei.

Rate and timing of vegetative growth, flowering and fruit development of Persoonia virgata (Proteaceae)

Persoonia virgata R. Br. is harvested from the wild in both its vegetative and flowering stages. There has been no systematic study published on the annual growth cycle and anecdotal reports are conflicting. The growth pattern, flowering and fruit development of P. virgata in its natural habitat was recorded monthly for two consecutive years. The main growth period occurred in late spring-mid-autumn (November-May) when the shrubs were producing little or no fruit. Very few open flowers were observed at the site over the 2 years, with only 6.7 and 12.7% of stems bearing open flowers in January and February 1996, respectively. A second study of flowering on container-grown shrubs showed that individual flowers were open for only 2-5 days, with individual stems taking 3-8.5 weeks to complete flowering. The main fruit growth period occurred from May to September, and in June and July 1996 the total fruit set per stem was 41.6 and 36.1%, respectively. The fruit took at least 6 months to develop during which vegetative growth was minimal. The harvesting of plants in the flowering or fruiting stages removes the annual seed crop, which may reduce regeneration of this obligate seed regenerator and threaten its survival after fire.

Plant genotype, juvenility and mechanisms of inhibition of rooting Persoonia virgata R. Br. cuttings

Persoonia virgata is an endemic shrub of Australia that is being bush-harvested for its foliage and sold on the domestic and export flower markets. The limiting factor to the cultivation of many desirable Persoonia species has been the extreme difficulty in developing a reliable propagation system. This study investigated the effects of cutting type, maturity of the stock plant, and genotype, on the rooting of P. vilgata cuttings. It was found that juvenile cuttings rooted significantly better than mature cuttings. Some juvenile seedling genotypes yielded no rooted cuttings, whereas others produced up to 90% rooting. No anatomical barrier to root formation was discovered. High performance liquid chromatography showed differences in the abundance of unidentified compounds in cuttings, related to season and to genotypic differences in rooting abilities. A possible seasonal rooting inhibitor was present in some genotypes. The potential for selection of genotypes with improved rooting ability has been demonstrated.

Floral ontogeny of brunonia australis (Goodeniaceae) and calandrinia sp. (Portulacaceae)

Floral ontogeny of Brunonia australis Sm. ex R.Br. (blue pincushion) and Calandrinia sp. (not yet fully classified) was investigated by scanning electron microscopy to assist further efforts for manipulating flowering of these potential floriculture crops. This is the first work to study floral initiation and the stages of flower development for these species. Floral initiation of B. australis commenced 28 days after seed germination when grown at 25/10 or 35/20°C (day/night) under long days (11 h of ambient light at 553 ± 45 µmol m–2 s–1, plus a 5-h night break at <4.5 µmol m–2 s–1). Leaf number at floral initiation reflected differences in the accumulated thermal time between treatments so that about double the number of leaves formed at 35/20°C. This suggested differing temperature responses for leaf and phenological development, and that leaf number was not a good indicator of floral initiation. For Calandrinia sp., floral initiation commenced 47 days after seed germination when grown at 25/10°C. Hot temperatures (35/20°C) inhibited flowering; indicating a vernalisation requirement. For B. australis, the pattern of floret development was centripetal, with flowers organised into five whorls. Four bracts surrounded each flower, whereas the sepals, petals and stamens showed a pentamerous arrangement. A central style was terminated by an indusial stigmatic presenter. Flowers of Calandrinia sp. consisted of four whorls, namely two sepals, 8–10 petals, numerous stamens produced centrifugally and a central syncarpous gynoecium with four stigmatic branches.

Reproductive biology and intergeneric breeding compatibility of ornamental Portulaca and Calandrinia (Portulacaceae)

Portulaca grandiflora Hook and P. umbraticola Kunth (Portulacaceae) are popular garden annuals, and have been bred for improved ornamental value. However, limited research has been published on hybridisation of Portulaca, with no reports on intergeneric hybridisation. Calandrinia balonensis Lindley and Calandrinia sp. nov. (not yet fully classified) are floriferous Australian Portulacaceae species, with potential as novel flowering pot plants, and are potential candidates for breeding with ornamental Portulaca. We studied the reproductive biology of these four species and breeding compatibility for reciprocal crosses of P. grandiflora × C. balonensis (2n = 18) and P. umbraticola × C. sp. nov. (2n = 24). All four species produced seeds for intraspecific outcrosses. P. grandiflora and C. sp. nov. are partially self-compatible whereas P. umbraticola and C. balonensis are highly self-incompatible. Autogamy was detected only for P. grandiflora. Reciprocal crosses of P. grandiflora × C. balonensis and P. umbraticola × C. sp. nov. with similar chromosome numbers did not produce seeds, primarily because of pollen–pistil incompatibility that prevents pollen-tube growth within the stigmata. Methods to overcome hybridisation barriers of these species combinations need to be established to create novel products for ornamental horticulture.

Influences of precooling and silver thiosulphate on leaf abscission of two forms of rice flower

Abstract Helichrysum diosmifolium , commonly called rice or sago flower, is an Australian wildflower being exported to Japan. Leaf drop occurring 10, 12 and 14 days after harvest from flowering stems of both broad and fine-leafed forms was reduced by silver thiosulphate (STS) pulsing. The most severe leaf drop occurred when flowering stems were not precooled and were kept dry until the assessment stage of the experiment. Severe leaf drop occured 10, 12 and 14 days after harvest in flowering stems that were kept in water during precooling. The vase life of the two forms behaved in different ways to the treatments. The fine-leafed form had its longest vase life when it was precooled and the stems kept dry during this treatment. However, for the broad-leafed form the longest vase life was achieved by pulsing stems with STS (4 m M , 15 min), followed by precooling with stems kept in water.